Referring to FIG. 1, a conventional electrochemical biosensor 1 includes a substrate 11, a pair of sensing films 121 formed on the substrate 11, a pair of connecting terminals 13 respectively coupled to the sensing films 121, and an insulating layer 14 formed on the substrate 11 and defining a sensing window 12 for accessing the sensing films 121. A receptor, which can specifically bind to an analyte in a liquid sample, can be immobilized on the sensing films 121. By applying the liquid sample onto the sensing films 121 and applying a voltage between the sensing films 121 via the connecting terminals 13, a monitored steady state current can be utilized to detect the analyte concentration in the liquid sample. However, when the applied voltage is greater than a redox potential of the receptor, the receptor will lose its ability to perform specific binding with the analyte. Under such circumstance, a minimum amount of analytes in the liquid sample that can be detected by the biosensor (also known as the detection limit) is limited due to the limited amplitude of the applied voltage. Moreover, when analyte concentration variations between samples are relatively small, differences between the monitored steady state currents corresponding to the samples may not be large enough to be detected.